1. Technical Field
This invention relates to a stacked battery module formed by connecting non-aqueous electrolyte secondary batteries in series. The present invention also relates to an assembly of stacked battery module formed by connecting a plurality of such stacked battery module in series or in parallel and a battery pack formed from such stacked battery module. Particularly, the present invention relates to a stacked battery module, an assembly of stacked battery module and a battery pack of non-aqueous electrolyte batteries such as lithium ion secondary batteries showing a high energy density, for which a charging operation can be stopped before the security thereof is damaged by some abnormality that arises during the charging operation.
2. Related Art
Lithium ion secondary batteries are being popularly used in mobile phones, notebook-sized personal computers, camcorders, etc. because they provide an energy density higher than other secondary batteries such as nickel cadmium batteries and nickel hydride batteries. Additionally, lithium ion secondary batteries are finding applications as power sources for electric tools and uninterruptible power supplies and as main or auxiliary power sources for bicycles and automobiles.
A lithium ion secondary battery comprises a negative electrode made of a material such as carbon adapted to dope/dedope lithium ions and a positive electrode made of a transition metal oxide containing lithium such as lithium cobalt oxide, lithium nickel oxide or lithium manganese oxide. A non-aqueous electrolyte obtained by dissolving lithium salt such as LiPF6 is used as the electrolyte of the lithium ion secondary battery.
Lithium ion secondary batteries are provided with a protection circuit for avoiding an overcharged state because the internal pressure of the battery can rise and/or heat generation can take place to damage the battery due to deposition of lithium and/or decomposition of non-aqueous electrolyte when the battery is overcharged.
A stacked battery module formed by connecting a plurality of lithium ion secondary batteries in series and a battery pack formed by using such stacked battery modules are charged by applying the total charging voltage, which is the sum of the charging voltages of the unit batteries of the stacked battery module formed by connecting the unit batteries in series. However, if there is a unit battery whose impedance has risen or whose capacity has fallen for some reason or another in the stacked battery module, the unit battery whose impedance has risen or whose capacity has fallen can get into an overcharged state. Thus, each unit battery has to be controlled for the charging voltage by means of a protection circuit. Various techniques have been proposed to date to control the charging voltage.
The techniques that have been proposed so far include one for detecting both the abnormally overcharged battery, if any, and the abnormal condition of the charger of a battery that is formed by connecting battery units in series, each of which battery units has one or more than one unit batteries connected in series (see, for example, JP-A-11-98702) and one for using a charging circuit that can fully charge all the unit batteries connected in series while preventing them from being overcharged (see, for example, JP-A-2000-92731, JP-A-2000-50516).
Thus, the use of a protection circuit for monitoring each unit battery and preventing it from falling into an overcharged state is indispensable when lithium secondary batteries are connected in series and when a plurality of lithium secondary batteries are connected in parallel for use. However, an overcharged state can arise to endanger the stacked battery module when an abnormal condition takes place in the protection circuit that operates at the time of charging the lithium secondary batteries.
In view of the above identified circumstances, it is therefore the object of the present invention to provide a battery laminate formed by connecting a plurality of unit batteries using non-aqueous electrolyte such as lithium ion secondary batteries in series or connecting a plurality of unit battery groups formed by connecting unit batteries in series in parallel and a battery pack formed by using such stacked battery modules that can prevent from falling into a dangerous condition even when the protection circuit of the charging apparatus falls into an abnormal condition to give rise to an overcharged state.